C/1999 S4: Hubble Optical
Images
From July 5 to 7, NASA's Hubble Space Telescope
Imaging Spectrograph tracked comet C/1999 S4 (LINEAR).
The first photograph (left) shows a dramatic increase
in its brightness. The next image (middle) shows a wave
of newly created dust from the outburst flowing into
the atmosphere, or coma, of gas and dust around the
comet's core. The image on the right, shows a chunk of
material (bright dot behind comet) that broke off the
nucleus and is trailing in the comets tail. For more
information on the Hubble images.(Credits: NASA, H.Weaver and
P.Feldman (Johns Hopkins Univ.), M.A'Hearn (Univ. of
Maryland), C.Arpigny (Liege Univ.), M.Combi (Univ. of
Michigan), M.Festou (Obs. Midi-Pyrenees), and G.-P.
Tozzi (Arcetri Obs.))

Schematic showing comet LINEAR
orbit.
Comet LINEAR was discovered on September 27, 1999. Its
closest approach to Earth occurred July 23, 2000 at a
distance of 35 million miles. Its closest approach to
the Sun occurred July 26, 2000 at a distance of 71
million miles. LINEAR is an acronym meaning Lincoln
Near Earth Asteroid Research.(Credit: Larry Koehn)

Updated Chandra Image of Comet
C/1999 S4
Chandra's image of Comet LINEAR (originally released
in July 2000, see #4 below) has been updated to
incorporate new data that brings out the faint extended
emission around the comet and remove certain processing
artifacts.(Credit: NASA/SAO/C.Lisse,
S.Wolk, et al.)

Original Chandra Image of Comet
C/1999 S4 From July 2000.
On July 14, 2000 the Chandra X-ray Observatory imaged
the comet repeatedly for a total of 2 1/2 hours and
detected X-rays from oxygen and nitrogen ions. The
details of the X-ray emission, as recorded on ACIS,
show that the X-rays are produced by collisions of ions
racing away from the Sun (solar wind) with gas in the
comet.(Credit: NASA/SAO/C.Lisse,
S.Wolk, et al.)